Avalanche Forecast
Issued: Dec 23rd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
Stephen Holeczi,
We have a complex snowpack that varies quite a bit across the region. Consider this when choosing the type of terrain you want to expose yourself to. Avalanche control on Mt. Dennis in Yoho Thursday, and the area will be closed to all activities.
Summary
Weather Forecast
Alpine winds from the West will stay elevated Thursday, and alpine temperatures will stay slightly warmer (-4 to -5C) than valley bottoms (-6 to -8C), No new snow is in the forecast until the weekend. Winds look like they will decrease Friday and Saturday.
Snowpack Summary
Winds from a variety of directions have blown the 30-60cm of snow from the past week into wind slabs at higher elevations. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 50cm and ~80 cm respectively. The decomposing Nov crust/facets sits at the bottom of the snowpack. Height of snow at tree line is 80-150cm.
Avalanche Summary
Avalanche control Tuesday and Wednesday produced mixed results from no result to size 3. Most were storm slabs, sometimes stepping down to persistent layers. A few deeper releases on the Nov 5th crust/facets Tuesday including a skier remote in the Watermelon Peak area. Reports of explosive controlled new wind slabs from the ski hills today.
Confidence
Due to the number and quality of field observations
Problems
Wind Slabs
New wind slabs started to form Wed. and will continue to build Thurs. These are mainly found in the alpine but have been reported at treeline as well. The winds have been from many different directions so slabs may be found on a variety of aspects.
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There are a variety of weaker layers down ~50-80cm depending on the area. These are the Dec 7 and 13th layers of facets, suncrust, and isolated surface hoar. Their reactivity is a bit sporadic but treeline seems to be the biggest culprit.
- Dig down to find and test weak layers before committing to a line.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
We have had a few observations of avalanches stepping down to the Nov. 5 crust and facets. This is a problem with higher uncertainty, and is most prevalent in shallow snowpack areas where the layer has weakened over time.
- Be cautious in shallow snowpack areas where triggering is more likely.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 24th, 2020 4:00PM
